The first step was attitude, and I hope you have put some effort into it. If you have, then you are miles forward in your journey.
The next step is closer physical affection.
Before you're ready to incorporate this, I hope you have really invested the time in step one, and that you are paying attention to your Mom. You can't rush this. Remember, employ small incremental steps, and be sure of a solid foundation before you begin to build on it. If you're not sure, wait. There is a little risk in this step - not much - but you don't want to take any chances of raising her defensive screens. You lose nothing by waiting, and putting more effort into good interaction with her. But, if you think you're ready...
I want you to hug her tight. No more of those foot-away-back-patting and awkward hugs. Arms around her waist. Bring her in to your body. Hug her tight. Don't worry if she feels something down there (ahem). She won't mention it, and you won't mention it. Don't grind into her, understand, just hug her tight. Full body contact. Don't hold it too long - it's just a hug, remember? You are transitioning from an innocent hug to a lover's hug, so tell her you love her.
That worked pretty well, didn't it? She liked it. You liked it. From now on, that is your baseline. A good, tight full-body lover's hug.
When I'm around, make it a little less, understand? When I'm not where I can see, make it closer and more intimate. You don't ever want to go back to those stiff, uncaring hugs, but you want the hugs I can see to be just a little less intense. Remember, you are trying to establish the idea that there is a difference in how you two interact when I'm there, and when I'm not. You want to establish and build on the idea that the two of you have a secret level in your relationship. Once you get her to understand that your close affection is something that I should not know about, you are a major step forward in reaching your goal.
With that intimate hug, you introduced closer intimate physical contact between the two of you. So, you want to build on that. When you're out shopping or just walking around, hold her hand. Don't make it a grab-her-hand-and-never-let-go thing. Just sometimes reach down and take her hand. That may not mean much to you, but it will speak volumes to her.
Don't be afraid of your dick. We'll talk more later about this, but I suspect whenever you're around her you will be, well, up and ready. Don't be afraid of that, or shy about it but, in fact, encourage it. Don't call attention to it, yet, but when you hug her, let her feel it. When you're around her, don't try to hide it or run to another room when it pops up. When you're with her and hard, keep eye contact and reach down to surreptitiously adjust it. Don't overdo this - do it rarely, but don't be afraid to do it if you have to. Her eyes will be on your eyes, but she'll know what you're doing. Believe me, she knows it's there and she's interested in it. I'll bet you catch her checking you out sometimes. If you don't make it an issue, she won't either, and she'll be pretty flattered, curious, and turned on. You just want her to know that when she's around, your dick is hard.
Joke with her. Play with her. Have conversations with her. Make her know you enjoy being with her, and let her enjoy being with you. Have private jokes, just between the two of you. Maybe it's something like that slice of pizza you shared when you were shopping, and you agreed that I shouldn't know about it. You want to have secrets with her, harmless at first, but secrets.
When you're sitting on the couch watching television, sit beside her and sometimes take her hand. You don't want to be overly affectionate when I'm there, because you don't want to embarrass her or make her feel vulnerable in doing something I might see and misunderstand. But when I'm not there, and I promise I'll give you plenty of opportunities, be a little more affectionate. Keep it light. You don't want her to think there is anything behind it - you're just showing affection.